Do you get at least 30 minutes of moderate physical exercise most days of the week? If you did, your brain would appreciate it. Evidence is mounting that physical activity -- specifically aerobic exercise -- improves memory and various other brain functions and may lower the risk of dementia.

Most of the evidence comes from a mountain of studies on rats and mice, but data collected on people is growing. It shows convincingly that you can preserve your mental skills as you age, regain some of the horsepower you’ve already lost, and even help to stave off Alzheimer’s disease and other forms of dementia.

“There’s quite a bit of evidence now suggesting the beneficial effects of moderate intensity exercise on the brain,” says Kirk Erickson, a neuroscientist at the University of Pittsburgh. He is at the forefront of research on exercise and the brain. “This includes maintaining the structure of the brain and preventing deterioration, but also improving the actual functioning of the brain as well.”

Even better, you don’t need to run a marathon. You simply need to engage in some sort of aerobic exercise -- any rhythmic activity that engages the large muscle groups of the body -- long enough to raise your heart rate. Think a brisk 45-minute walk, three or more times per week. Or enough laps in the pool so that you can feel your pulse thumping. “You don’t have to be a member of a gym,” Erickson says. “Primarily we’re measuring people who just walk.”

And it’s not too late if you have spent much of your later years in couch potatohood. Aerobic exercise, even if started later in life, still improves brain function.

Living large

People who are more fit age better in terms of the brain’s physical condition (structure) and how well it performs mental tasks (function). And remarkably, it appears that some regions of the brain important to thinking and memory are actually larger in fit individuals.

This means people who have remained physically fit as adults may start out with more “cognitive reserve” as they enter the second half of life. Statistical studies suggest these folks are less likely to develop dementia -- or perhaps they will develop it at a later age than less-fit people.

Physical activity hits multiple risk factors for memory impairment. It reduces stress and improves sleep, both of which affect memory function. Exercise lowers the risk of stroke. And it helps to control blood sugar, which at high levels can damage the brain, according to some studies.

Neurobiological studies on rats and mice provide some clues to the biological details. For example, exercise supports the growth and survival of new brain cells in the hippocampus, the pair of seahorse-shaped regions in the brain that play a central role in memory. Exercise also releases brain chemicals that may stimulate the growth of blood vessels.

The hippocampus link

In human research, the link between exercise, the hippocampus, and memory is more recent. Erickson led a team that has made the connection for the first time in a study in the October 2009 issue of the journal Hippocampus.

The team performed magnetic resonance (MR) imaging on about 160 people, aged 59 to 81. They were also assessed for aerobic fitness in a treadmill test. And they were scored on a task called spatial memory, or the ability to recall the position of dots flashed on a computer screen.

The results: The fitter the volunteers were, the better they performed on the spatial memory test. The MR scans also revealed a link between hippocampal size and fitness. Statistical analysis showed that fitness could account for 8 percent of the larger volume in the right hippocampus and 12 percent in the left.

Statistics also delivered the capping finding of the study: a “triple association” between aerobic fitness, hippocampal volume, and spatial memory. That means we can be more confident in the conclusion that exercise supports memory by producing a healthy hippocampus.

“This link between exercising and better memory performance is well known from animal studies,” Erickson says. “But what are the brain regions involved? This study is really the first time we’ve been able to put all this together.”

The fitness prescription

So exercise is good for the mind and memory. But Erickson and other researchers in the field still have some important gaps to fill. “What is not definitively known is how much exercise is needed to see these effects," Erickson says. "Are there any particular types of exercise that are needed?”

Another important question is how exercise interacts with other lifestyle factors that influence healthy aging: intellectual activity, social interaction, and diet. The research can’t tell us, for example, whether it’s better to go on a solitary nature walk or join a water aerobics class. The aerobics class would combine exercise and social interaction. Is there synergy?

Asking such questions presents a technical challenge because it involves measuring the effect of changing two aspects of a person’s lifestyle. That demands much larger studies than it takes to measure the effect of exercise alone.

These studies must be done, Erickson says. “It’s difficult to run just one of them,” he says. “But people are realizing that these things aren’t independent of each other. There can be some additional benefit of combining these interventions.”

Factoring in all the influences of lifestyle on cognitive function might help explain why people age so differently. “In next few years, we’re going to see more and more studies trying to combine these factors,” Erickson predicts.

Big numbers

The era of larger and more definitive studies on exercise and the brain is already underway. Erickson is a member of a team led by psychologist Arthur F. Kramer at the University of Illinois, Urbana-Champaign, that just completed the largest study to date. About 150 older adults engaged in supervised exercise three times per week for a year. Their brains were scanned before, at 6 months, and after the study.

Erickson says the study is large enough to answer key questions. “We’ll hopefully get some answers regarding whether or not starting to exercise when you’re 70 years old can actually reverse some of the deterioration and cognitive issues that have arisen.”

If the results are clear and positive enough, they might just get more people onto the walking path or into the pool. The prescription for healthy brain aging? Take two laps around the park and repeat in the morning.

RESOURCES

“Aerobic fitness is associated with hippocampal volume in elderly humans,” by Kirk I. Erickson (Hippocampus, October 2009, Vol. 19, no. 10, pp. 1030-1039). Abstract available via PubMed.

“Be smart, exercise your heart: exercise effects on brain and cognition,” by Charles H. Hillman and others. (Nature Reviews Neuroscience, 2008, Vol. 9, pp. 58-65.) Abstract available via PubMed.

“Exercise effects on cognitive and neural plasticity in older adults,” by Kirk Erickson & Arthur F Kramer (British Journal of Sports Medicine, published online October 16, 2008.) Abstract available online.

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